It is conventional to examine a biological sample, for example a faecal sample, by placing it in a first tubular receptacle which is then closed by a filter medium. The first tubular receptacle may be attached to a second one in axial alignment such that the sample will pass into the second receptacle from the first through the filter. Filtration can be achieved simply by standing the assembly with the first receptacle uppermost or it may be encouraged by shaking the joined receptacles and/or placing them in a centrifuge. Following the completion of filtration, particles trapped by the filter and/or precipitated to the closed end of the second receptacle can be removed for analysis.
A double-receptacle filtration system of this kind is particularly, although not exclusively, suitable for the treatment of faecal samples where it is desired to isolate and remove for analysis of parasites, their eggs and larvae which may be present in the sample. The handling of such samples is unpleasant and presents biological hazards so that the "closed" double-receptacle filtration system is particularly attractive. Hitherto, however, the filter medium used has most commonly been a disc of woven material or a molded lattice which can be fitted across the open mouth of the first receptacle. This is liable to become clogged and occluded by larger particles suspended in the sample, such as pieces of undigested food Moreover if the double-receptacle is placed in a centrifuge this will tend to drive particles through the filter into the second receptacle. For this reason filtering and centrifuging are normally done separately and this two-stage operation is time consuming and labor intensive, as well as representing a hazzard to the operator when the two receptacles are disconnected.